(1) Field of the Invention
The present invention relates to solid stick cosmetics such as eyebrow and eyeliner, which are powdery (easy to become powdery) and which are excellent in usability and have a sufficiently good color tone, and a production process for the same.
(2) Description of Prior Art
Conventional solid stick cosmetics are obtained by kneading a colorant and a filler with waxes such as oil & fat, wax, fatty acid, and hydrocarbon as a binder and molding the mixture to a stick. Since they are oily when they are applied to skin, and the waxes are softened in a place of high temperatures, not only physical odd is felt upon the application thereof to skin, but also it is difficult to maintain the shape of the stick cosmetics. Further, since the stick cosmetics are very liable to be broken in using them if the amounts of waxes are increased in order to obtain a sufficiently large breaking strength, it results hardening the stick cosmetics and causing them to lack in adhesion to skin and smoothness.
Thus, since the solid stick cosmetics using waxes for a binder have oiliness peculiar to the waxes, a powdery (a dry and smooth feeling like powder) use feeling can not be obtained, and it has been difficult to satisfy a sufficiently large breaking strength and a good application feeling to skin at the same time.
Accordingly, stick cosmetics which are intended to obtain a powdery use feeling without using waxes are investigated. Proposed are those using water soluble adhesive pastes such as CMC (carboxymethyl cellulose) for a binder (Japanese Patent Application Laid-Open No. Sho 59-44305) and those using gypsum for a binder (Japanese Patent Application Laid-Open No. Sho 59-93014).
However, since the binders are extremely hardened in the stick cosmetics using these binders, an application feeling to skin is very stiff. Further, applying these binders to thin articles such as eyebrow and eyeliner makes them very breakable, and increasing the amount of the binder in order to obtain a sufficiently large breaking strength makes it impossible at all to apply them to skin.
That is, it is difficult, for stick cosmetics in which water soluble adhesive pastes such as CMC or gypsum are substituted for waxes as a binder in order to obtain a powdery use feeling, to satisfy a sufficiently large breaking strength and a good application feeling at the same time. Further, stick cosmetics which satisfy a sufficiently large breaking strength and a good application feeling at the same time without using waxes are investigated as well, and proposed are those in which clay is used for a binder and the clay is sintered (Japanese Patent Application Laid-Open No. Sho 61-176513) and those in which a pore-forming material is used to prepare a more porous sintered substance (Japanese Patent Application Laid-Open No. Sho 61-197507). The invention disclosed in Japanese Patent Application Laid-Open No. Sho 61-176513 provides the stick cosmetics in which an inorganic pigment dispersed in a powder form is incorporated into a sintered substance of clay having a porous skeleton formed by providing sintering treatment. According to the descriptions of the above publication, the term "porous" means "the larger the porosity is, the better the touch and applicability in use tend to become, and the smaller and more minute the porosity is, the more the strength tend to increase". In the end, disclosed by the above publication is a sintered substance having a porosity of a level of 50 to 90%.
That is, while a sintered substance of clay provides a sufficiently large breaking strength, it is hard and therefore difficult to be applied to skin. However, turning it to a porous sintered substance provides a stick cosmetic which satisfy a sufficiently large breaking strength and a good application feeling at the same time.
The invention disclosed in the claims of Japanese Patent Application Laid-Open No. Sho 61-176513 described above can not provide a desired color tone and quality the stick cosmetics have to provide.
The control of a porosity is indispensable in order to satisfy a good application feeling and a sufficiently large breaking strength at the same time, but it is very difficult to obtain a sintered substance having such a preferred porosity of a level of 50 to 90% as described in the above publication only by changing temperatures in sintering treatment and a use proportion of clay and a powdered pigment as described in the above publication. In order to obtain the porosity falling in such the range, needed are means by which an excipient and a molding aid of various resins added for molding are removed by burning them in an oxidation atmosphere in sintering treatment, or pores are formed by removing them by depolymerization in an inert atmosphere, as described in the examples of the above publication, or means by which pores are intentionally formed by using the pore-forming agent disclosed in Japanese Patent Application Laid-Open No. Sho 61-197507.
However, in the method for removing various resins added for molding by burning them in an oxidation atmosphere in sintering treatment, colored pigments are oxidized as well in the sintering treatment, and therefore when colored pigments which are susceptible to oxidation, such as black pigments including black iron oxide, carbon black and titan black are used, they are discolored or faded. Accordingly, a desired color tone can not be developed.
In the method for removing various resins by depolymerization in an inert atmosphere, the resins are practically turned into carbides and remains in stick cosmetics. Accordingly, it is very difficult to remove them completely. As a result thereof, the stick cosmetics become blackish, and therefore a desired color tone can not be developed. Further, even when resins which leave relatively less carbides, such as polymethyl methacrylate are used, the carbides remain, though only slightly, in the stick cosmetics, and a method for burning the resins in an oxidation atmosphere has to be resulting employed in order to remove them completely. Furthermore, these carbides not only prevent a desired color tone from being developed but also form variant primary substances as well. Further, in depolymerizing polymethyl methacrylate, the resulting monomers have a high toxicity, which causes a serious problem on the safety of cosmetics.
In a method in which pores are formed by using a pore-forming agent and removing it by chemical treatment after sintering treatment as disclosed in Japanese Patent Application Laid-Open No. Sho 61-197507, there is no concern about remaining carbides as described above. However, it is very difficult to remove the pore-forming agent from stick cosmetics by the chemical treatment. As a matter of fact, when removing the pore-forming agent by such the method, a method in which the pore-forming agent is eluted from stick cosmetics by chemicals is used. Accordingly, the forms of the stick cosmetics are broken, and it is almost impossible to remove completely the pore-forming agent while maintaining the forms thereof.
Since the pore-forming agent results in remaining in the stick cosmetics as an impurity, not only sufficient pores are not formed but also a problem on quality is presented in terms of safety as cosmetics.
The methods described in Japanese Patent Application Laid-Open No. Sho 52-97399, Japanese Patent Publication No. Sho 53-13491 and Japanese Patent Publication No. Sho 57-50741 are proposed as a method for obtaining the sintered substance of an inorganic pigment having a sufficiently good color tone. However, all of these methods apply to pigments or fine particles and do not apply to stick cosmetics. In other words, while fine particles used for cosmetics having a sufficiently good color tone can be obtained when these methods are used, it is impossible to mold fine particles to sticks and maintain the form thereof, and therefore solid stick cosmetics can not be obtained at all.
The method described in Japanese Patent Application Laid-Open No. Sho 61-225107 is proposed as a method for obtaining solid stick cosmetics having various color tones.
However, this method causes a color change by heat treatment, and therefore when two or more kinds of colorants are contained at the same time, the respective colorants cause independently characteristic color changes, for example, if a brown color is intended to develop with black iron oxide and red iron oxide, the heat treatment discolors independently black iron oxide and red iron oxide, and the desired brown color can not be developed. In short, the method in which colors are changed by heat treatment limits the resulting color tones and makes it very difficult to obtain various color tones necessary for stick cosmetics.